This invention relates to catalyst systems useful for polymerizing alpha-olefins and particularly relates to a supported titanium halide catalyst component and a catalyst system containing such component and more particularly to a solid catalyst component which can be modified to yield varying particle morphologies.
Magnesium-containing supported titanium halide-based alpha-olefin polymerization catalyst components are now well known in the art. Typically, these catalysts are recognized for their performance based on activity and stereospecificity. However, commercial olefin polymerization, especially gas-phase alpha-olefin polymerization, requires additional catalyst attributes for economical large-scale operation. Specifically, polymer morphology, typically dependent upon catalyst morphology, many times is critical. Included in good polymer morphology is uniformity of particle size and shape, resistance to attrition and an acceptably high bulk density. Minimization of very small particles (fines) typically is very important, especially in gas-phase polymerization to avoid transfer or recycle line pluggage. Very large particles also must be avoided to minimize formation of lumps and strings in the reactor. A suitable catalyst should produce a polymer with minimum particles having average diameter less than 150 microns (fines) or greater than 850 microns. Depending upon the polymerization process used, at times it is desirable to use solid catalyst particles of different size distributions.
Another property which is important commercially is maintenance of an acceptably high bulk density. Typically, this property is measured in pounds per cubic foot of polymer. One approach to improve morphology control as described in U.S. Pat. No. 4,540,679 is to solubilize a magnesium species with carbon dioxide in an alcohol solvent. U.S. Pat. No. 4,612,299 describes formation of magnesium carbonates and magnesium carboxylate supports. U.S. application Ser. No. 186,359, filed Apr. 25, 1988, corresponding to EP250,230, assigned to a common assignee, discloses a titanium, magnesium, halide, organic complex polymerization catalyst.
The present invention incorporates a series of catalyst formation process steps described in U.S. Ser. No. 186,359, filed Apr. 25, 1988 which produce a catalyst with exceptionally high activity and stereospecificity combined with very good morphology with an ability to modify the particle size distribution of the resulting solid catalyst depending on its method of preparation.
Supported, magnesium-containing, titanium-containing, electron donor-containing olefin polymerization catalysts now are well known in the art. Use of carbon dioxide in preparing a magnesium-containing support has been described in the aforementioned U.S. Pat. No. 4,540,679. Also, in a different context use of carbon dioxide was described in U.S. Pat. Nos. 4,246,383; 4,244,838; 4,529,715; and 4,530,915. Treating alcoholic solutions and suspensions of alkaline earth alcoholates with sulfur dioxide was noted in Chemical Abstracts, Vol. 76, 853050v (1972). Forming a soluble magnesium species has been described in U.S. Pat. Nos. 4,315,874; 4,399,054; 4,071,674; and 4,439,540. Examples of use of silicon compounds in formation of a catalyst component include U.S. Pat. Nos. 4,071,672; 4,085,276; 4,220,554; and 4,315,835. Tetrahydrofuran (THF) has been described variously to complex a magnesium chloride species (e.g., U.S. Pat. Nos. 4,482,687, 4,277,372, 3,642,746, and 3,642,772 and in European Pat. 131,832); as a modifier in a cocatalyst (e.g., U.S. Pat. Nos. 4,158,642 and 4,148,756); and as a solvent (e.g., U.S. Pat. Nos. 4,477,639 and 4,518,706).
U.K. Patent Published Application GB 2111066 A describes an olefin polymerization catalyst component containing magnesium, titanium, halogen and an ester selected from the group consisting of esters of polycarboxylic acids and esters of polyhydroxy compounds, is obtained by contacting a liquid hydrocarbon solution of (i) a magnesium compound with (ii) a titanium compound in the liquid state to form a solid product or first preparing a liquid hydrocarbon solution of the magnesium compound (i) and the titanium compound (ii) and then forming a solid product therefrom, said reaction of forming the solid product being carried out in the presence of (D) at least one electron donor selected from the group consisting of monocarboxylic acid esters, aliphatic carboxylic acids, carboxylic acid anhydrides, ketones, aliphatic ethers, aliphatic carbonates, alkoxy group-containing alcohols, aryloxy group-containing alcohols, organic silicon compounds having an Si-O-C bond and organic phosphorus compounds having a P-O-C bond, and during or after the formation of the solid product, and contacting the solid product with (E) an ester selected from the group consisting of esters of polycarboxylic acids and esters of polyhydroxy compounds. The final catalyst in use also contains (B) an organometallic compound of a metal selected from the group consisting of metals of Groups I to III of the periodic table, and (C) an organic silicon compound having an Si-O-C bond or Si-N-C bond such as an alkylalkoxysilane.
U.S. Pat. Nos. 4,298,718, 4,476,289, 4,544,717 and 4,636,486 all are directed to a catalyst formed by reacting a titanium compound with an "active magnesium dihalide." U.S. Pat. Nos. 4,107,413, 4,107,414 and 4,336,360 are related to the catalysts previously described in U.S. Pat. Nos. 4,298,718, 4,476,289, 4,544,717, and 4,636,486 in that an element of each claim is a catalyst component formed by reacting an "activated magnesium dihalide" with titanium tetrachloride. U.S. Pat. Nos. 4,226,741 and 4,331,561 are related and are directed to a catalyst prepared by reacting a magnesium dihalide with a halogenated titanium compound and an electron donor. U.S. Pat. Nos. 4,410,589 and 4,330,649 are related and are directed to a product of (1) a magnesium compound "in the liquid state" having no reducing ability, in the presence of (2) an electron donor with no active hydrogens, with (3) a halogen-containing compound in the liquid state. U.S. Pat. No. 4,290,915 is directed to a solid titanium catalyst component containing, magnesium, titanium and halogen in which a liquid hydrocarbon is present in an amount from 1 to 10% or 1 to 25% depending on the component's "uniformity coefficient."
U.K. Patent 1,554,340 describes an olefin polymerization catalyst component formed by reacting a magnesium alkoxide, an organic electron donor and a titanium halogen compound. EP 86,643 describes an olefin polymerization catalyst component formed from a magnesium compound, a titanium compound, an electron donor such as a dialkyl phthalate. A liquid magnesium compound may be reacted with a liquid titanium compound in the presence of an electron donor and may be further reacted with a titanium compound and electron donor. The catalyst system described contains an ester of phosphorus acid with an alcohol of 2 to 4 carbon atoms. EP 86,645 describes an olefin polymerization catalyst formed from a component containing titanium, magnesium, halogen and an electron donor, an organoaluminum compound and a polyamino compound. The electron donor may be a dialkyl phthalate, diisobutyl phthalate or diethyl phthalate.
U.S. Pat. No. 4,442,276 describes an olefin polymerization catalyst component composed of a solid titanium catalyst component obtained by reacting tetravalent titanium, magnesium, halogen and an electron donor with an organosilicon compound having a Si-O-C bond. Applicants' material is not formed according to the procedure disclosed. U.S. Pat. Nos. 4,472,524, 4,473,660 and 4,522,930 described olefin polymerization catalysts formed by reacting an aluminum alkyl, an electron donor such as a silicon compound containing an Si-O-R group and a solid titanium-containing compound supported on a magnesium halide which could be formed by reacting magnesium with an alcohol or with a hydrocarboxyl halide and an alcohol or reacting a magnesium mono-or dialcohol or carbonate with a halogenating agent.
However the specific combination of steps taught in this invention to produce a catalyst with extremely advantageous properties have not been disclosed in the above-cited references.